The proposed research is concerned with a joint examination of psychological signs of cognitive behavior and physiological signs of brain function manifested by cerebral potentials recorded from the human scalp. Long latency positive potentials, referred to as P300 components, reflect CNS processes involved in information reception and decision activity. Such components are also elicited by the absence of a stimulus, when absence conveys significant information to the subject. Components elicited by stimulus absence, referred to as emitted potentials, are apparently dependent upon memory and internal timing mechanisms. Because emitted potentials are signs of endogenous CNS activity alone, they provide an opportunity to study mental-cognitive processes per se in a controlled manner. The properties of emitted potentials, the circumstances governing their occurrence, and their relationship to evoked potentials will be investigated in the context of experiments in which 1) the object of the experiment is detection of near-threshold intensity stimuli; 2) stimulus presence or absence provides informational feedback on performance of a prior task; 3) explicit time estimation is required. In one paradigm, information will be conveyed to the subject by a sequence of two events. The object will be to study emitted and evoked potentials associated with a) activation of memory storage by the first event, and b) the subject's analysis of total information within the sequence subsequent to the occurrence of the second event.